This invention relates to a refrigeration system, and in particular, to a system having at least two evaporators served by a common refrigerant compressor whereat different forms of expansion devices are employed to control the flow of refrigerant to each of the evaporators.
In some refrigeration systems it is at times necessary to have a single compressor connected to at least two evaporators having different refrigeration loads thereon. Essentially, the single refrigerant compressor provides vaporous refrigerant to a single condenser, with the high pressure liquid formed in the condenser flowing to the multiple evaporators of the system.
In some applications, it is desirable to employ a fixed-orifice or capillary type expansion device for controlling the flow of refrigerant to the evaporator whereas in other applications it is desirable to employ a thermal expansion valve for controlling the flow of refrigerant. Each of the two types of expansion devices provides different benefits and also has different operating characteristics. As used herein the terms "fixed-orifice" or "capillary type" shall be considered as describing equivalent devices since both of these expansion devices function in substantially the same manner within the systems of the type falling within the scope of the present invention.
For example, a thermal expansion valve cannot tolerate any refrigerant vapor bubbles in the flow of refrigerant therethrough. Essentially, liquid refrigerant having entrained vapor bubbles results in a thermal expansion valve operating in a totally inefficient manner.
A fixed-orifice expansion device functions to change the high pressure, high temperature refrigerant upstream thereof into low pressure, low temperature refrigerant downstream thereof. The quantity of refrigerant passing through the capillary expansion device is primarily dependent upon the pressure differential of the refrigerant across the device.
As the refrigeration load on the evaporator associated with the fixed-orifice expansion device decreases, the device tends to permit excessive refrigerant flow to the evaporator resulting in incomplete vaporization of the refrigerant exiting the evaporator. An accumulator is utilized to collect the liquid refrigerant leaving the evaporator. Eventually, a sufficient quantity of refrigerant will be gathered in the accumulator whereby vaporous refrigerant bubbles will be entrained in the refrigerant exiting from the condenser. The entrained bubbles serve an important function. The bubbles throttle the flow of refrigerant through the fixed-orifice device until an equilibrium or balance is reached between the refrigeration load and refrigerant flow. The vaporous refrigerant bubbles are formed in the refrigerant passing to the capillary type expansion valve device as a result of incomplete refrigerant condensation.
When it is desired to provide a single compression device in association with two or more evaporators, one of which is connected to a capillary expansion device and the other to a thermal expansion device, problems in obtaining overall efficient operation of the refrigeration system are created. The vaporous bubbles formed in the refrigerant mixture delivered from the condenser when the refrigeration load on the system is relatively low will create operating problems if the mixture is delivered to the thermal expansion valve, yet is required to regulate the flow of refrigerant through the capillary expansion device.